Select the Arcade mission from the main selection screen and then, on the next screen that allows you to choose between Time Attack or Story mode, shoot outside of the screen. If the cheat has worked, you'll see the word 'Easy' appear over the Story Mode option. Now select it and start playing and you'll have five lives and a lot more time.
At the Main Title Screen, shoot at the center of the R in the word CRISIS. Then, shoot twice directly inside the crosshairs, which is next to the word TIME. If your shots are quite accurate, a Cheat Menu should appear, giving you access to a few extra options to choose from. You can then begin your next game with nine lives.